1. Field of the Invention
The present invention relates to a thin-film magnetic head with a heater, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic disk drive apparatus with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, a thin-film magnetic head performs writing information into and reading information from a magnetic disk, which is rotated by a spindle motor. The thin-film magnetic head has an inductive write head element and a magnetoresistive (MR) read head element, both of which are formed on a slider substrate fixed at a top end section of a suspension of a HGA. While read or write operation, the thin-film magnetic head is moved to the desired position of the magnetic disk by an arm, which can swing.
The thin-film magnetic head aerodynamically flies with some height, which is called magnetic spacing dMS above the rotating magnetic disk, while in operation. The flying thin-film magnetic head writes information into the magnetic disk using magnetic field generated by the inductive write head element, and reads information from the magnetic disk using the MR read head element, which senses the magnetic field generated by the magnetic disk.
Recently, track width of a thin-film magnetic head rapidly becomes narrower to satisfy the requirement forever increasing data storage capacities and densities in today's magnetic disk drive apparatus. If the track width becomes narrow, signal recoding and reproducing ability in a magnetic head element to the magnetic disk will degrades. To avoid such a degradation in the signal recording ability and/or the signal reproducing ability, recent thin-film magnetic head tends to have a smaller magnetic spacing dMS. Because the shorter the magnetic spacing dMS becomes, the stronger the intensity of magnetic field at the thin-film magnetic head is. Recent years, the thin-film magnetic head is designed to use about 10 ns magnetic spacing dMS.
However, while in write operation, a coil layer of the inductive write head element generates the Joule heat, and the heat caused by eddy-current loss is generated in upper and lower pole layer. An overcoat layer expands thermally, and TPTP (Thermal Pole Tip Protrusion) phenomenon occurs, where the magnetic head element protrudes toward the magnetic disk surface. Due to TPTP, the surface of the slider, where the magnetic head elements are placed, has a curvature towards the magnetic disk. When a designed value of the magnetic spacing dMS is very small, thermal asperity may occur from the change in the electric resistance value of the MR read head element caused by frictional heat that is generated when the protruded part of the MR read head element contacts the magnetic disk surface.
In order to avoid this thermal asperity, methods to control magnetic spacing dMS has been proposed. For example, U.S. Pat. No. 5,991,113 discloses a slider having a transducer which is a magnetic head element, where a heater is formed adjacent to the transducer in the slider substrate or between the slider substrate and the transducer. The heater is heated by electrical current, and the transducer is protruded using the difference of thermal expansion coefficients between a transducer-formed region including the protection layer and the slider substrate to control the magnetic spacing dMS.
Also, US patent publication No. 2003/174430 discloses a thin-film magnetic head structure, which reading and writing elements are brought close to a magnetic disk surface by expanding a thermally expansive element. In this structure, a heater and a thermally expansive element are positioned in a pair. Reading and writing elements are brought close to the magnetic disk surface by distorting an overcoat layer using a distortion force obtained by heating the thermally expansive element.
Further, US patent publication No. 2003/99054 discloses a thin-film magnetic head having a heating means provided in the opposite of an air bearing surface (ABS) of a magnetic head elements. While the magnetic head elements are in operation, the heating means is heated so that the magnetic head element protrudes toward the ABS direction to adjust the magnetic spacing dMS.
However, such thin-film magnetic heads with a heater and/or a thermally expansive element have disadvantages, because the MR read head element is sensitive to the heat.
As mentioned above, with increasing data storage capacities and densities, high performance and high reliability are required for the components of the magnetic disk drive apparatus. Especially the MR read head element needs to sense weak magnetic field with high resolution in narrower track width environment, thin-film with nanometer-scale are laminated, and the size is reduced, while electric current density applied to the MR read head element becomes extremely high for getting the high outputs. Therefore temperature of the MR read head element is high even in the normal operation condition. Furthermore output of the MR read head element strongly depends on the temperature with increasing the sensibility. Therefore thermal control, especially limiting temperature rise, is mandatory for stable read operation.
However, prior art mentioned above, the heater causes further temperature rise of the MR read head element, and it worse the performance of read operation.
In case of the slider disclosed in U.S. Pat. No. 5,991,113, since the heater is formed adjacent to the transducer in the slider substrate or between the slider substrate and the transducer, the heat propagates to whole transducer-formed region including slider substrate and the protection layer. Generally, a shield layer inside the MR read head element is made of metal, and its coefficient of thermal conductivity is higher than the overcoat layer, which is made of insulating material. Therefore the heat is easy to propagate to the MR read head element, which is sandwiched between the shield layers. Furthermore, in case of the thin-film magnetic head disclosed in US patent publication No. 2003/174430 and US patent publication No. 2003/99054 mentioned above, the heater is placed close to the MR read head element, the heat propagates to the MR read head element through the shield layer more easily.
Since prior art does not have a means to prevent the heat evolved by the heater or heating means from propagating to the MR read head element, in consequence, the temperature of the MR read head element sometimes exceeds allowable maximum, so that reading performance becomes worse than desired level.
Furthermore, the heater described in U.S. Pat. No. 5,991,113 is placed inside the slider substrate, or is contacted with the slider substrate, and heating means described in US patent publication No. 2003/99054 is placed close to the slider substrate. Therefore most part of the heat evolved by the heater is absorbed by the slider substrate, which coefficient of thermal conductivity is relatively high, and emitted to outside of the thin-film magnetic head. That means thermal efficiency that causes the TPTP phenomenon becomes lower. To deal with this issue, if heating is up, it makes temperature of the MR read head element higher, because the amount of heat propagated to the MR read head element via shield layer increases, in consequence, it makes the reading performance of the MR read head element worse.